1. Field of the Invention
The present invention relates to an optical print head and an image forming apparatus including the optical print head.
2. Description of Related Art
Recently, there has been known an exposure device in which an optical print head is configured by using an OLED (Organic Light-Emitting Diode) as a light source of graded index rod lens array (SLA (registered trademark); Selfoc (registered trademark) Lens Array).
In a case of an LED print head (LPH) using an LED (Light Emitting Diode) as a light source, since a plurality of light source blocks are connected to each other to make a light emitting element in a single line, there is a problem of uneven light emission due to variety in luminous point between the light source blocks and placement error between the light source blocks. On the other hand, a light source of OLED can be manufactured as a single light source, and thus can solve the uneven light emission which is the largest problem of LPH.
Furthermore, compared with the element using the LED as the light source, the element using the OLED as the light source has a great advantage in dot position gap and is suitable for high image quality.
Conventionally, in the field of the optical print head which uses the OLED as the light source and the SLA as an imaging optical element, there is disclosed a configuration in which the light emitting substrate of the OLED is directly bonded to the SLA (for example, see Japanese Patent Application Laid Open Publication No. 2001-26139).
Since the light emitting substrate of OLED is exposed to high temperature during the manufacturing process thereof, glass with a particularly small linear expansion coefficient needs to be adopted as glass to be a base substrate. That is, the substrate of the OLED is a material with a very small linear expansion coefficient which is largely different from that of the SLA, and thus a relative position gap due to temperature changes in the surrounding environment has been a large problem.
For example, in a technique described in the above Japanese Patent Application Laid Open Publication No. 2001-26139, there is a risk that the relative position gap occurs due to the temperature changes of surrounding environment since the light emitting substrate of the OLED and the SLA which have very different linear expansion coefficients are bonded to each other.
Specifically, since the SLA is originally for focusing light which is emitted from a single light source through a plurality of rod lenses, the amount of light and light focusing are uneven according to the arrangement pitch of the rod lens array. Accordingly, in conventional SLAs, the whole uneven light emitting is evened mainly by correcting the amount of light for each light emitting dot.
However, the amount of light shifts from the optimum value when the relative position gap occurs between the light emitting substrate of OLED and the rod lens array of SLA since the light amount correction value for each light emitting dot is calculated and stored when the optical print head is manufactured. Accordingly, the amount of light cannot be accurately corrected for each of the light emitting dots, which leads to image deterioration as a result.